1. Technical Field
The invention relates to electronic communications networks. More particularly, the invention relates to a method and apparatus for providing 10Base-T/100Base-TX link assurance in an electronic communications network.
2. Description of the Prior Art
Commonly used electronic communications networks include Ethernet (also referred to as 10Base-T) and Fast Ethernet (also referred to as 100Base-TX). Such networks, also referred to as local area networks (LANs), operate in accordance with generally accepted protocols that are defined by standards groups, e.g. IEEE 802.3. A 10Base-T and 100Base-TX network allows communications over a point-to-point full-duplex medium, referred to as a link segment, between communicating devices that typically comprise link partners, i.e. local devices, such as data terminal equipment (DTE) or a repeater, at opposite ends of the link segment.
Such networks provide a feature referred to as auto-negotiation (see IEEE 802.3u.), which is used by the physical layer entity 14 (PHY) (see FIG. 1) to automatically select the speed, type, and duplex mode of a link established between link partners at nodes in the network. FIG. 1 is a block schematic diagram that shows the location of the auto-negotiation function 26 within a link partner in an electronic communications network in accordance with IEEE 802.3u-1995. The auto-negotiation function is provided at the Physical Layer 12 of the OSI reference model shown on FIG. 1. The PHY is that portion of the physical layer (12, see FIG. 1) between the medium dependent interface 16 (MDI) and the media independent interface 18 (MII) and consists of the physical coding sublayer 20 (PCS), physical medium attachment 22 (PMA) and, if present, the physical medium dependent sublayers 24 (PMD).
The auto-negotiation process determines the highest possible level of functionality possible, where both nodes negotiate to a common highest level. For example, if a half-duplex 10Base-T node is connected to a full-duplex 100Base-TX node, negotiation is adjusted to half-duplex 10Base-T. If both nodes are capable of operating a full-duplex, then the link is established in 10Base-T full-duplex mode.
Auto-negotiation is accomplished through the use of Fast Link Pulses (FLPs), which comprise a group of link-pulses that are concatenated together to create a data stream. Each data bit in the FLP stream is used to define either the node's technology ability, remote fault, acknowledgement, or next page functions. FLPs are discussed in greater detail in IEEE 802.3u, Clause 28, which is incorporated herein by this reference thereto. Auto-negotiation also includes a function referred to as parallel detection (IEEE 802.3u, section 28.2.3.1, page 244-5).
Presently there are many 10Base-T and 100Base-TX devices that do not comply with the auto-negotiation specification set forth in IEEE 802.3u, Clause 28. These devices are hereinafter referred to as legacy devices. Such devices only link to other legacy devices or auto-negotiating devices that incorporate the parallel detect function.
There are also many devices that provide an auto-negotiation feature, but are still not 100% compliant with IEEE 802.3u, Clause 28. Such devices do not auto-negotiate with each other well. Such devices are nonetheless available on the market and are used in and/or with various other products to which such devices must link to establish and maintain a satisfactory information exchange session. Thus, many 100Base-TX devices on the market advertise support for the IEEE 802.3u, Clause 28, auto-negotiation specification. However, some of these devices are not compliant with the specification, and therefore create interoperability problems (i.e. ability to link and connect) between devices that are compliant with the IEEE specification.
For example, when a 100Base-TX IEEE auto-negotiation compliant devices tries to connect to an auto-negotiation capable but non-compliant device, auto-negotiation fails and the devices never link unless the device vendor provides manual switches to force connection. In this case, physical interaction with the hardware, and network knowledge, are required to configure the system correctly and make the two devices interoperate. Thus, one solution to the problem of linking such disparate devices is to manually toggle a switch provided with the device. This forces the device into a particular mode of operation. However, this approach does not allow customers to upgrade their LAN from 10Base-T to 100Base-TX easily.
Existing devices that use auto-negotiation are available. The availability of such devices, however, does not assure linkability because at least some of such devices are non-compliant with IEEE 802.3u, Clause 28.
Other existing devices use an algorithm that is referred to herein as software parallel detect. The algorithm is as follows:
1. Turn on the 100base-TX transceiver for a given length of time. PA1 2. Check for link status. If linked, then set PHY to 100base-TX and exit. PA1 Otherwise, go to step 3. PA1 3. Turn on 10base-T transceiver for a given length of time. PA1 4. Check for link status. If linked, then go to step 5. If no link, go to step 1. PA1 5. Turn on 100base-TX transceiver for a given time to reverify that the devices cannot link at 100base-TX. (If a short LAN cable is used, then 100base-TX idle can appear to a 10base-T receiver as a valid link.) PA1 6. Check link status. If linked, then set PHY to 100 base-TX and exit. If no link, then set PHY to 10base-T and exit.
The algorithm allows detection of link partners that support 100base-TX and/or 10base-T, but that do not support auto-negotiation. Because these devices link at 10base-T half duplex and 100base-TX at halt duplex, they do not allow linking at full duplex. Further, such devices can corrupt a 10base-T network while trying to link at 100base-TX.
Another version of the algorithm deletes Steps 5 and 6 above, and exits at Step 4 if the devices are linked.
It would be advantageous to provide a technique for establishing a link between disparate network entities in a 10Base-T/100Base-TX network.